Lire et écouter en anglais sur http://www.pilotworkshop.com/tips/special_vfr_clearance.htm

Il faut la demander au contrôleur pour dégager sa responsabilité

extrait
SVFR can be an effective tool to allow a VFR aircraft to land or depart in conditions below basic VFR. On those days when there is a stubborn 900 foot cloud deck over the airport but you can see into the next county, a SVFR clearance can let you fly towards better weather. That is the most important point about a SVFR – always make sure you are flying towards better weather or have an escape plan. You never want to be trapped in marginal conditions

Voir aussi
https://en.wikipedia.org/wiki/Special_visual_flight_rules
et
http://thinkaviation.net/special-vfr-clearance/